Obama returns to arms control -- just in time

President Barack Obama's call during the State of the Union address to reduce the threat of nuclear war could not have been more timely. The day before the president spoke, North Korea tested a primitive nuclear device, and the following day reports surfaced of Iranian attempts to buy technology that would greatly speed up its production of weapons-grade uranium.

Mr. Obama's remarks focused on cutting the U.S. and Russian strategic arsenals in a way that maintains their deterrent function but reduces the chances of a conflict breaking out by accident or miscalculation. The New START Treaty the president negotiated with Russia in 2010 caps the number of long-range missiles at 1,550 by 2018, but Mr. Obama and his generals believe that number could be cut even further without endangering national security. Currently, each side has about 1,700 such missiles in its arsenal.

The president has the support of the nation's military, which recognizes that the nature of the threats we face has changed since the end of the Cold War. The U.S. no longer needs a massively redundant force to guarantee a devastating response to a Russian first strike. Today, the likelihood of war with Russia has receded to the point where it's more likely a conflict would break out as a result of a technical glitch or human error than by design. Keeping thousands of warheads on hair-trigger alert only compounds that danger.

In the 21st century, the most challenging threats are likely to come not from today's great powers but as a consequence of the proliferation of nuclear weapons and technologies among smaller nations and failed states in politically unstable parts of the world, such as Pakistan and North Africa, or from rogue regimes like North Korea and Iran. In this environment, the greatest danger will be the possibility that a nuclear explosive could fall into the hands of terrorists or other nonstate actors who, by definition, cannot be deterred by the threat of massive retaliation.

Yet we can hardly claim the moral high ground in urging such states to restrain their nuclear ambitions so long as our own arsenals are bristling with arms. Nor do we need 1,700 nuclear warheads to deter an attack from Iran or North Korea. The logic of such an asymmetrical conflict, in which our conventional weapons alone have the capacity to wipe out their entire military, political and economic infrastructure, makes the reduction of a few hundred nuclear warheads irrelevant.

Mr. Obama has gone on record as saying the world won't be safe until these terrible instruments of destruction are banished from the face of the Earth. Complete nuclear disarmament may not be achievable today, nor perhaps for decades to come, but the president is right to continue pressing for steps leading to that goal. The likelihood of a catastrophic nuclear exchange with Russia or China may have diminished substantially since the end of the Cold War, but it has not disappeared entirely.

Until that happens, the U.S. will need to maintain a credible deterrent force, but it need not be on the scale of the past. Mr. Obama hopes to reach a private understanding with Russian President Vladimir Putin regarding the size of his proposed cuts rather than negotiate a new treaty that would require approval by a Senate polarized along partisan lines. It's ironic that the president should have to seek an end run around Senate Republicans in order to build on the legacy of a former Republican president, Ronald Reagan, who negotiated the nation's first Strategic Arms Reduction Treaty with Russia and who famously declared that a nuclear war cannot be won and must never be fought.

Mr. Obama clearly would like to be remembered as a president who helped pull the world a step further back from the abyss, and if he manages to rid the planet of another thousand or so U.S. and Russian nuclear weapons, he will have gone a long way toward fulfilling the promise embodied by the Nobel Peace Prize he was awarded in 2009. We hope that remains a top priority for his administration during the remainder of his second term.